The prime purpose of this research utilizing chronic experiments in awake baboons whose gallbladder (GB) remains in situ and functioning will be delineation of the role of the gallbladder in the production of lithogenic bile, the most critical step in the pathogenesis of cholesterol gallstones. Emphasis will be upon the interactions of gallbladder function, bile salt physiology (secretion rate S, synthetic rate T, pool size P and enterohepatic circulation rate C) and bile lithogenicity (bile salts, cholesterol and phospholipid expressed on triangular coordinates RC). Whether or not normal gallbladder function exerts a controlling mechanism over hepatic secretion of bile will be determined by documenting 1) if gallbladder volume (GBV) and/or gallbladder pressure (GBp) control the partition ratio (R) of hepatic bile secretion 2) if variations in R occur with fasting or after stimulation with emptying (GBE) or filling (GBF) and 3) if the interactions of GBV, GBp, R, GBE, and GBF are reflected in a passive (as predicted) way on S, T, P, and C and therefore on RC rather than as controlling mechanism. Whether or not abnormal GB function can be considered a primary or a contributing cause for the production of lithogenic bile will be determined by documenting if 1) gallbladder stasis and 2) increased biliary pressure can influence R, GBE, GBF, S,T,P, C or RC. Whether or not modification in bile salt physiology can influence gallbladder function so as to make it either a primary or a contributing cause of lithogenic bile will be determined by documenting if 1) decrease P and/or 2) slower C can change GBV, GBp, R, GBE, or GBF. BIBLIOGRAPHIC REFERENCES: Wittenberg, J., Maturi, R., Williams, L.F., Teplick, S., Preblud, S., O'Brien, J., and Small, D.M.: Intravenous cholangiography in the Rhesus monkey. Part I: Determination of optimal iodipamide dose during a one-hour infusion. Invest. Rad. 11:45, 1976. Small DM, Beaudoin M, Shaffer E, O'Brien J, and Williams LF: The Ballbladder and the enterohepatic circulation. In: Advances in Bile Acid Research, Part IV: Physicochemistry of Bile Acids, 293-298, 1975 (ed. S. Materm, J Hackenschmidt, P. Back and W. Gerok) FD Schattauer Veriag, NY.